fallout

1. 1. The slow descent of minute particles of debris in the atmosphere following an explosion, especially the descent of radioactive debris after a nuclear explosion.
   2. The particles that descend in this fashion.
2. An incidental result or side effect: "Other social trends also have psychiatric fallout, and the people who suffer can't afford treatment" (Martha Farnsworth Riche).

Whenever radioactive materials become airborne, either from a nuclear device detonation or from a nuclear release accident, the resultant contaminated atmospheric plume will ultimately return radioactivity to the Earth's surface. Material settling from the radioactive plume and its subsequent surface deposition is known as radioactive fallout.

Radioactive materials consist of unstable atoms which emit gamma rays, beta particles, or alpha particles. These emissions—rays and particles—are unique in that they cause ionizations in neighboring atoms. The energy of the emitted radiation and subsequent ionizations can be a cause of concern if absorbed by living systems. See also Alpha particles; Beta particles; Gamma rays; Radioactivity.

Fissioning of uranium and plutonium produces isotopes of about 70 different atoms; each atom may have several different isotopic forms. Examples of daughter products are the isotopes of elemental strontium, which are efficiently produced in nuclear fission. The isotope strontium-90 (⁹⁰Sr) has a 28-year half-life, while ⁸⁹Sr is produced in slightly higher concentrations but has a half-life of only 50 days. In addition to the differing half-lives, each isotope emits a unique radiation spectrum. The two strontium isotopes emit beta particles of different energies. Other isotopes such as cesium-137 (¹³⁷Cs, half-life 30 years) and iodine-131 (¹³¹I, half-life 8 days) emit both beta particles and gamma rays. See also Cesium; Iodine; Isotope; Strontium.

Atmospheric fallout can be scavenged by rainfall. Wet deposition, involving washing out of atmospheric fallout, can increase local deposition patterns. This was the case following the Chernobyl accident, where local rainfall in Belarus, Ukraine, and Russia washed high concentrations of radioactive iodine and cesium out of the plume and onto the spring pasture. Radioactive iodine and cesium are relatively volatile and were more easily “boiled” out of Chernobyl's burning core. Cesium is a congener of potassium and therefore is fairly uniformly distributed throughout the body once inhaled or ingested. The result is a whole-body radiation dose. Furthermore, the energetic gamma-ray emission from ¹³⁷Cs adds a source of external radiation from surface deposits on the ground. These factors, in addition to its long half-life and relatively high concentration, make ¹³⁷Cs the major long-term contamination concern from fallout. For example, although the Chernobyl accident occurred in 1986, precautions must still be taken against potential intake doses of ¹³⁷Cs: inhalation doses can occur when burning wood from contaminated trees, and consuming mushrooms grown in contaminated forests delivers an ingestion dose.

Levels of ¹³¹I in the plumes of radioactive fallout are of particular concern. With an 8 day half-life and a strong beta- and gamma-ray emission, this radionuclide concentrates almost exclusively in the thyroid gland. Recent dose reconstructions in the United States show that the 1950s and 1960s fallout radiation doses from ¹³¹I were large enough to have increased the risk for thyroid cancer, especially in children.

In 1955, the United Nations established the Scientific Committee on the Effects of Atomic Radiation, due to concern over possible risks from fallout. It issues comprehensive reports about every 5 years and has collected and documented the world's literature on radioactive fallout and, more recently, on possible radiation consequences. See also Atomic bomb; Nuclear explosion; Nuclear fission; Nuclear fuels; Nuclear reactor.

n. 1. the precipitation to earth of radioactive particulate matter from a nuclear cloud.

2. the particulate matter itself.

See the Introduction, Abbreviations and Pronunciation for further details.

For more information on fallout, visit Britannica.com.

The settling to the earth's surface of radioactive fission products from the atmosphere after a nuclear explosion.

(DOD) The precipitation to Earth of radioactive particulate matter from a nuclear cloud; also applied to the particulate matter itself.

Tutor's tip: If the "fallout" (negative side effects of any action) from a bad business deal is bad enough, the partners might "fall out" (to break with someone as a result of a quarrel) with each other.

Dansk (Danish)
n. - radioaktivt nedfald, nedfald af radioaktivt støv

Nederlands (Dutch)
radioactieve neerslag, langdurige consequentie

Français (French)
n. - retombées (radioactives), (fig) retombées

Deutsch (German)
n. - radioaktiver Niederschlag, negative Konsequenzen

Ελληνική (Greek)
n. - ραδιενεργά κατάλοιπα, (καθομ.) καβγάς, τσακωμός

Italiano (Italian)
fall-out

Português (Portuguese)
n. - radiação (f) que afeta uma área após explosão nuclear

Русский (Russian)
осадки, непредвиденные последствия

Español (Spanish)
n. - lluvia radioactiva

Svenska (Swedish)
n. - nedfall, biverkningar

中文（简体）(Chinese (Simplified))
原子尘的降下, 原子尘, 辐射性微尘

中文（繁體）(Chinese (Traditional))
n. - 原子塵的降下, 原子塵, 輻射性微塵

한국어 (Korean)
n. - 낙진

日本語 (Japanese)
n. - 降下, 放射性降下物, 副産物, 死の灰

العربيه (Arabic)
‏(الاسم) السقط , الغبار الذري المتساقط‏

עברית (Hebrew)
n. - ‮נשורת גרעינית, ההשפעות השליליות של מצב וכד'‬

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